A color television camera must have control of the individual red, green, and blue black levels, the individual red, green, and blue white levels and also a master control of all black levels. The master black level control should not, however, disturb the white levels in any way. To simply raise the black levels when adjusting for light conditions also proportionately raises all of the video levels the same percentage. The white level at the other extreme of the video which is set to provide the desired white level for the light conditions is raised by the raise in master black level. To raise the black levels alone requires, therefore, at the same time a reduction of the gain. In the past the white levels were maintained constant when the master black is changed by using non-linear amplifiers or by sampling a special white test pulse with a feedback servo AGC amplifier.
The non-linear amplifier does not provide a truly constant white level as the master black is adjusted and the feedback system tends to be complex and unstable. It is also desirable from a hardware point of view to make this system fit a digital format and be usable in a digital control system such as described in co-pending applications: Ser. No. 894,011, filed Apr. 6, 1978, entitled "TELEVISION CONTROL SYSTEM," and now U.S. Pat. No. 4,170,024 of Robert A. Dischert, Ser. No. 894,010, filed Apr. 6, 1978, entitled, "SETUP CONTROL UNIT FOR TELEVISION CAMERAS," and now U.S. Pat. No. 4,167,022 Thorpe et al, Ser. No. 894,009, filed Apr. 6, 1978, entitled, "CONTROL FOR A TELEVISION CAMERA," of Robert A. Dischert et al, and Ser. No. 894,008, filed Apr. 6, 1978, entitled "AUTOMATIC SETUP SYSTEM FOR TELEVISION CAMERAS," and now U.S. Pat. No. 4,158,208 of Robert A. Dischert.